COLUMN DROPS- My column drops come with a standard 1 1/2'' diameter hole for 1 1/2" columns. Some fitting required for specific applications. Comes in raw finish
 
You should drill and tap a set screw into bottom of column. I drill 2 into mine. I do not drill and tap these for the simple reason that my drops can be turned around for a simpler and clean look. Again much thought into my designs for different applications. I leave it to you to customize. I designed my 3" drop for my race car as \I wanted to put a dash indicator light into the drop. This service can be done in shop at a extra cost for dash light and bulb.
Note: I do not drill and tap mounting holes. This should be don’t by a qualified professional so your column mounts firm